You isolate nuclei from three different eukaryotic species. You treat the samples in exactly the same way
Question:
You isolate nuclei from three different eukaryotic species. You treat the samples in exactly the same way (adding same amount of enzyme, buffer and time) to partially digest the chromatin with micrococcal nuclease, extract the DNA, and run it on a gel. You see the pattern below:
Lane | Approximate size of bands (in base pairs) |
1 | 200, 400, 600, 800 |
2 | 180, 360, 540, 720 |
3 | 190, 380, 570, 760 |
a- Knowing that the core-DNA in all cell types is the same what is your explanation for the difference in size in the patterns you observe (shown below):
b- If you digested each of the three samples more thoroughly, what would the pattern look like? [Be specific and indicate what the size of the bands would be]
c- An explorer discovers a strange new species of plant and sends some of the plant tissue to a geneticist to study. The geneticist performs the kinds of experiments as described above in (b) except that: After digestion with nuclease 120-bp fragment of DNA are seen.
Analysis of the histone core reveals histones in the following proportions:
H2A 33.3%
H2B 33.3%
H3 0% [no histone H3 found]
H4 33.3%
On the basis of these observations, what conclusions could the geneticist make about the probable structure of the nucleosome in the chromatin of this plant? Be specific in describing the nature of the nucleosome: which histones form the core (1pt), how many of each are in there (1pt) and how much core-DNA is around it.
d-The geneticist also found H1 and a new histone H7 when histones were extracted from all of the chromatin (not just the nucleosome). What do you think the role of the new histone H7 would be in this new plant species?
Fundamentals of biochemistry Life at the Molecular Level
ISBN: 978-0470547847
4th edition
Authors: Donald Voet, Judith G. Voet, Charlotte W. Pratt